1. Technical Field
The present invention relates to a piezoelectric driving device and a driving method thereof, and a robot and a driving method thereof.
2. Related Art
A piezoelectric actuator (piezoelectric driving device), which vibrates a piezoelectric body to drive a body to be driven, does not need a magnet or a coil, and accordingly, it is used in various fields (for example, see JP-A-2004-320979). A basic configuration of this piezoelectric driving device is a configuration in which four piezoelectric elements are arranged on each of two surfaces of a reinforcing plate to have two rows and two columns, and accordingly, eight piezoelectric elements in total are provided on both sides of the reinforcing plate. Each piezoelectric element is a unit in which a piezoelectric body is interposed between two electrodes and the reinforcing plate is also used as one electrode of the piezoelectric element. A protrusion which comes in contact with a rotor, which is a body to be driven, to rotate the rotor is provided on one end of the reinforcing plate. When the AC voltage is applied to two piezoelectric elements diagonally disposed among the four piezoelectric elements, the two piezoelectric elements perform an expansion and contraction operation, and accordingly, the protrusion of the reinforcing plate performs a reciprocal operation or an elliptic operation. The rotor, which is a body to be driven, rotates in a predetermined rotation direction according to the reciprocal operation or the elliptic operation of the protrusion of the reinforcing plate. In addition, it is possible to rotate the rotor in a reverse direction, by switching the two piezoelectric elements to be targets of application of the AC voltage, with the other two piezoelectric elements.
In the piezoelectric driving device described above, since two diagonally disposed piezoelectric elements are connected in parallel, capacitance is large and a great current is necessary for driving. When the piezoelectric driving device is accommodated and used in a small space (for example, in a joint of a robot), wiring space may be insufficient in a case of the piezoelectric driving device using a piezoelectric body of the related art, and accordingly, it is desired to decrease the thickness of the piezoelectric body. However, since the capacitance is inversely proportional to a distance between electrodes interposing the piezoelectric body, the capacitance may increase, when the thickness of the piezoelectric body is decreased.